rails/rails — pull request #12632 by al2o3cr (2013-10-24 19:10:32+00:00)
Title: Always check to see if methods exist after calling define_attribute_methods

Addresses the bug isolated in #12607 where two threads that both dispatch into `method_missing` will result in only one of them successfully calling the newly-created method.

No idea how to test this, especially since the bug only appears in a threaded environment under very specific timing conditions.